In conventional shaft bearing structures for rotatably supporting a rotating shaft, the rotating shaft is rotatably fitted in a bushing, and the bushing is fitted in a hole formed in a supporting member. Specifically, both the inner surface of the hole of the supporting member and the outer surface of the bushing are made in the form of a circumferential surface so that they tightly contact each other.
Where a bearing structure is to be constructed by tightly fitting a bushing in a hole with each having a circumferential surface as described above, a high machining accuracy is required for machining the hole and the bushing. If some play is present in the fitting of both components, the rotating shaft will not be accurately supported and held at the desired position. Therefore, in the case of a printer wherein the rotating shaft of a platen and the guide shaft of a print head are to be rotatably supported, both shafts will not have the desired parallelism or they will be unstable such that high quality printing cannot be attained.
It is an object of the present invention to provide a shaft bearing structure in which a hole and a bushing can be tightly fitted with each other without the need for high machining accuracy.